Different animation lengths for each animation? (For FBX Export)
As far as I know the timelines range won't change based on how long your actions are in the action editor, but when exporting as an FBX the actions will retain the correct length based on where the first and last frames are so your walk cycle should show up as an animation clip with the 30 frame length this is how it has worked for me with Unity I am not familiar with Unreal though. I would also recommend saving your actions to a data-block otherwise you risk losing them.